1. Field of the Invention
The present invention relates to an exposure apparatus, and an exposure method, for performing direct exposure, on a relatively moving exposure target substrate, using a plurality of exposure heads.
2. Description of the Related Art
Generally, a wiring pattern on a wiring substrate is formed by exposing the substrate based on design data relating to the wiring pattern and by developing and printing the desired pattern on the substrate, followed by etching. During the exposure process, photomasks are usually used. More specifically, a photosensitive resin is applied over a substrate constructed by bonding metal foil as a conductive layer onto an insulating material, and a photomask with the desired wiring pattern drawn thereon is placed over it. By exposing the thus prepared substrate, the wiring pattern defined by the photomask is transferred to the photosensitive resin on the substrate. Thereafter, by performing the steps of developing, etching, plating, etc., the metal foil on the substrate is formed as the desired wiring pattern.
In an exposure method using such a photomask, the photomask is placed in intimate contact with the substrate prior to exposure; if, at this time, any foreign matter or stain remains adhering to the substrate, the shape of the foreign matter or stain is also transferred onto the substrate. The finer the wiring pattern drawn on the substrate is, the more sensitive the photomask is to foreign matter and staining and, therefore, particularly strict management of the photomask is required. Further, if the wiring pattern is changed or damaged, a new photomask must be produced. In this case, the photomask must be produced on a trial basis a number of times by making corrections to account for the expansion, shrinkage, distortion, displacement, etc. that can occur in the substrate. The resulting increase in production cost and time has been a great burden in the production of a wiring substrate.
On the other hand, a patterning method based on direct exposure that does not use photomasks has been proposed in recent years. According to this method, as corrections for expansion, shrinkage, distortion, displacement, etc. of the substrate can be made in real time, or in advance at the exposure data generation stage, significant improvements can be achieved, for example, in enhancing the manufacturing accuracy, increasing the manufacturing yield, shortening the delivery time, and reducing the manufacturing cost.
The patterning methods based on direct exposure include, for example, methods that form an exposure pattern by direct exposure using a Digital Micromirror Device (DMD), an electron beam exposure machine, or the like.
In the prior art, one example of the patterning methods based on direct exposure that use the DMD is disclosed in Japanese Unexamined Patent Publication No. 10-112579. According to the technique disclosed therein, when directly exposing the photoresist formed on an exposure target substrate, pattern data corresponding to the pattern to be exposed is generated and this pattern data is input to the Digital Micromirror Device (DMD), causing each of the micromirrors arranged thereon to tilt according to the pattern data and thereby changing the direction of the light, reflected by each micromirror on the DMD, as needed; the light thus controlled is projected onto the resist on the exposure target substrate to form an exposure pattern that matches the pattern data.
FIG. 8 is a diagram showing, by way of example, exposed areas formed by an exposure apparatus according to the prior art. In the figure, DMD micromirrors in each exposure head 100 constructed from the DMD are indicated by open circles (reference character Q). In this and other figures, the number of exposure heads, the number of micromirrors in each exposure head, and their relative sizes are shown for illustrative purposes only. As, usually, the entire area of the exposure target substrate 151 cannot be exposed by a single exposure head 100, a plurality of exposure heads 100 are arranged in a direction orthogonal to the direction of the relative movement of the exposure target substrate 151, and the exposure is performed using these exposure heads 100. In the figure, the area exposed by each exposure head 100 (hereinafter called the “exposed area”, indicated by reference numeral 152) is shown by oblique hatching. The area that can be illuminated by the micromirrors Q in each exposure head 100 is limited, and there occurs a spatial gap between each exposure head 100 due to the nature of its structure; here, if the gap between each exposure head 100 is large, an area left unexposed (hereinafter called the “unexposed area”, indicated by reference numeral 153) occurs on the exposure target substrate 151, as shown in FIG. 8. On the other hand, if the gap between each exposure head 100 is too small, an area (not shown) that simultaneously receives light from two adjacent exposure heads occurs on the exposure target substrate, and such an area is subjected to a larger amount of light than necessary compared with other areas.
Japanese Unexamined Patent Publication No. 2004-146789 discloses a technique that projects an equal amount of light over the entire exposure surface by moving a single exposure head back and forth for exposure in such a manner that adjacent exposed areas overlap each other.
However, in the exposure apparatus in which a plurality of exposure heads are arranged, the occurrence of the unexposed area due to the gap between each exposure head and the unevenness in the amount of projected light are undesirable because these can significantly affect the quality of the wiring substrate as a finished product.
On the other hand, the technique disclosed in Japanese Unexamined Patent Publication No. 2004-146789, which aims at projecting an equal amount of light over the entire exposure surface, requires that the exposure head be moved back and force, i.e., in two directions, not in one direction, relative to the exposure target substrate, and also that the movements be repeated a plurality of times; therefore, this prior art technique has the shortcoming that not only does it take a longer time to complete the exposure of one exposure target substrate, but the apparatus becomes complex in construction because of the provision of the mechanism for the back and forth movements.
Accordingly, in view of the above problem, it is an object of the present invention to provide an exposure apparatus and an exposure method for performing direct exposure using a plurality of exposure heads, wherein provisions are made to be able to accomplish the direct exposure at high speed while ensuring that no unexposed areas occur on the exposure target substrate moving relative to the exposure heads.